1. Field of the Invention
The present invention relates to molecular beam epitaxial technology, more particularly,, to a molecular beam epitaxial growth device and a molecular beam control method therein for exactly controlling a thickness and a composition of an epitaxial film.
2. Description of the Related Art
Recently, a laser diode and a high electron mobility transistor (HEMT) having a low noise and a high speed operation, which include an epitaxial growth (epitaxial film) formed by a molecular beam epitaxial growth device, have been developed and provided. For example, in accordance with the improvement of semiconductor integrated circuits comprising the HEMT device, it is required to exactly control the thickness or composition of the epitaxial film and to increase the yield rate of the semiconductor devices.
In the prior molecular beam epitaxial growth method (MBE: Molecular Beam Epitaxy), the intensity of a molecular beam is controlled by manually controlling the temperature of a molecular beam source cell to obtain a preferable epitaxial growth rate. Note, in order to measure the intensity of the molecular beam from the molecular beam source cell, a molecular beam flux measurement method using an ion gauge, an epitaxial growth rate measurement method by observing an oscillation of an RHEED (reflective high energy electron diffraction), or an epitaxial growth method for measuring a thickness of the film, have been used.
Note, even though the temperature of the molecular beam source cell is maintained at a specific value, the intensity of the molecular beam (molecular beam intensity) becomes varied in accordance with a decrease in quantity of the molecular beam source provided in the cell (molecular beam source cell), so that the epitaxial growth rate or the composition of the epitaxial film cannot be maintained at a constant preferable value. Therefore, in the prior art, the measurement of the molecular beam intensity must be frequently carried out and the cell temperature must be frequently corrected in accordance with the measured molecular beam intensity to maintain the epitaxial growth rate or the composition of the epitaxial film at the constant value.
Nevertheless, when correcting the cell temperature, the molecular beam epitaxial growth for forming a practical device (for example, HEMT device) should be carried out after stabilizing the molecular beam intensity or after again confirming the molecular beam intensity, and thus a long time is required before starting the molecular beam epitaxial growth for forming the HEMT device. Furthermore, the correction of the cell temperature is carried out in accordance with an operator's experience or intuition, so that the molecular beam intensity cannot be determined within the specific allowable range and the thickness or the composition of the epitaxial film cannot be exactly controlled.